The dilatation and effacement of the cervix uteri takes place both before and during labor. Second only to uterine contractions, it is necessary for the genesis of productive labor or nonproductive labor often coincides with excessive dilatation or the lack of proper dilatation. The resulting infant is often subnormal because of prematurity or anoxic birth. Cervical elasticity during labor would appear to be crucial to the control of labor. We are studying the stress-strain behavior of the rabbit cervix in the presence of the prostaglandins PGE2, PGF2 alpha, PGE1 and PGF2 alpha 16,16 dimethyl ester and urea in order to quantify and evaluate any possible contribution of these drugs to dilatation and to establish the validity of this animal model in research of this type. Non-pregnant, pregnant and labor-induced animals are being studied, as well as animals treated with prostaglandin antagonists. Strips of the cervix from these animals will be removed and stretched while the developing tension is recorded. This, a series of derived measurements may be obtained, one of which will be the stretch modulus, or measure of the elasticity of the tissue. With a single parameter of this sort, the various categories of animals will be statistically compared for variations, under treatment, of cervical elasticity.